Ribulose is a trivial name for the ketopentose (five carbon containing ketose) erythro-2-pentulose, usually found in nature as the D enantiomer, shown below in the furanose form (beware horrid ASCII graphics):-
O
/ \ CH2OH
/ \|
C C
\ /|
\ / OH
C----C
| |
OH OH
A derivative of ribulose, D-ribulose 1,5-bisphosphate (RBP or RuBP) is extrememly important biologically as a metabolite in the reductive pentose phosphate cycle in photosynthesis, where it is a substrate of the enzyme Rubisco.